This invention relates to an automatic valve intended for installation in the inlet of a thermostatic mixing device to stabilize its operation.
When a thermostatic mixing device, designed to be able to draw a certain flow rate, supplies an apparatus which, because of the high resistance that it creates against the flow, permits only the delivery of a much lesser flow rate, the pressure inside the thermostatic mixing device becomes close to the pressure in the water supply pipelines. If there develops, then, a considerable pressure difference between the hot water and the cold water supply pipelines, for example, due to the absorption of an apparatus with a high flow rate, such as a flowmeter flushing water device inserted on one of the pipelines due to the crosswise flow (the so-called cross-flow) that develops inside the thermostatic mixing device, the latter is in a state of instability or begins to oscillate with subsequent malfunctioning and instability of the temperature of the mixed water drawn by it.
This happens, for example, when a thermostatic mixing device, intended to supply in the absence of a strong resistance at the outlet a relatively high flow rate, such as, for example, 50 or 60 liters per minute at 3 bar, is used with a much lesser water delivery volume, for example, 9 liters per minute, which is limited by the resistance offered to the flow by certain apparatuses. This case occurs, in particular, when the thermostatic mixing device is installed to supply a multiple shower stall, each of which is equipped with its own exclusion device, while the user employs only one shower. More generally, the same case occurs when the thermostatic mixing device is arranged to supply a plurality of apparatuses or only one or a few of them are actually in operation.
This inconvenience can be remedied by installing a pressure compensator in the water supply pipelines up the line from the thermostatic mixing device. However, this additional apparatus increases the size and complexity of the installation also because it must be linked to both of the cold water and hot water supply pipes; that increases the cost of the apparatuses and the installation operations; besides, it is a rather delicate operation; it is easily subject to failure, especially due to deposits, and calls for a certain degree of maintenance. Its operation is not entirely satisfactory because, when the pressure in a pipeline is reduced, the compensator reduces the passage offered to the other pipeline and thus corrects the mixing ratio but modifies the flow rate that is actually drawn. Furthermore, under certain conditions, a pressure compensator can give rise to instability phenomenon.
According to Italian Patent Application No. 99 A 000 455, a thermostatic mixing device, controlled by thin obstruction plates situated at its inlet, can be arranged so as to function correctly, both when the maximum flow rates for which it was designed are drawn and also when reduced flow rates are drawn in the water supply lines of apparatuses with high flow resistance without entailing the above-mentioned inconvenience and without necessitating a pressure compensator by having the user arrange the thermostatic mixing faucet so as to adapt it to the various conditions of use or to the power supply of apparatuses that absorb flow rates that differ widely among each other.
This can be achieved by virtue of the fact that the entry passage openings of the thin blocking plates, which control the inlet pipes for the hot water and for the cold water, are shaped in relation to at least one of the pipelines for hot water and for cold water so as to present restricted passage cross-sections in a field adjacent to the occlusion position and large cross-section passage segments in the remaining regulating field.
In this way, when the thermostatic mixing faucet must supply one or several apparatuses that take a small flow rate, it is moved in its first regulation field, which takes place the moment the thermostatic mixing faucet is shifted from the occlusion position. The restricted cross-section of at least one of the entry passage openings then causes a relatively high pressure drop, although in the presence of a small flow rate caused by the high resistance at the outlet, and makes the thermostatic mixing faucet practically insensitive (to the effects of its stability) in contrast to the also significant pressure differences between the water supply pipelines. When, on the other hand, the thermostatic mixing faucet must supply apparatuses that absorb a large flow rate, it is moved into its second regulating field, which follows the first one. The large cross-section of the entry passage openings then makes it possible to draw the maximum flow rate that the thermostatic mixing faucet is capable of and, under these conditions, any possible, even significant, pressure differences between the water supply pipelines will not cause any inconvenience.
This provision ensures the perfect operation of a thermostatic mixing faucet, but it requires a maneuver, albeit a simple one, on the part of the user, and, furthermore, it cannot be applied to thermostatic mixing devices at whose inlet thin blocking plates are not installed.
In view of this, the primary purpose of this invention is to provide a valve intended to be installed at the inlet of a thermostatic mixing device of any kind, which would be suitable for automatically bringing about a performance in accordance with the one that is caused by the above-mentioned provision, causing a partial division of the passage cross-section, while the thermostatic mixing device supplies an apparatus with low water flow demand, which offers high resistance against the flow and, on the other hand, leaving the water supply line substantially clear, while the thermostatic mixing device supplies one or several apparatuses with a high overall water flow demand, which, together, gives rise to a low resistance against the flow.
Another object of the invention is to provide such an automatic valve, which would furthermore combine the function of a nonreturn valve as is required in many cases in which it is installed.
Yet another object of the invention is to provide such a valve, which would have a simple structure, be easy to manufacture, relatively cheap and so designed as to facilitate maintenance.
The first object of the invention is achieved in a valve intended for installation in the inlet of a thermostatic mixing device by virtue of the fact that the valve comprises a tubular body intended to be inserted in or constitute part of a pipe or connection for water supply, said body having a holding seat; a cursor that can be moved in said body with respect to said seat between a first position in which it at least partly occludes said seat, and a second position in which it leaves said seat substantially clear to permit the passage of a relatively large flow rate, said cursor being subjected, on the one hand, to the pressure of the water supply pipeline and, on the other hand, to the pressure existing inside said mixing device; and a spring that works on said cursor, pushing it toward said first position, said spring being dimensioned so that said cursor, with respect to said seat, will assume said first position or a position close to it under conditions in which the water flow demanded by said mixing device is relatively low, and will be shifted toward said second position or until it reaches it under conditions in which the water flow demanded by said mixing device is relatively high; wherein said cursor comprises means which, when said cursor assumes said first position or a position close to it, permit the passage of a flow rate sufficient only to supply a mixing device with a relatively low water flow demand.
In this way, when the water supply of an apparatus with low water flow demand tends to cause inside the thermostatic mixing device the establishment of a pressure close to the water supply pressure, the small difference between these pressures causes the cursor to assume a position close to said first position or coinciding with it and leaving clear a small passage cross-section, thus causing a pressure drop because of which the pressure that is actually established inside the thermostatic mixing device is limited and cannot give rise to any instability. When, on the other hand, the supply to apparatuses having a high overall water flow demand is such that inside the thermostatic mixing device a very low pressure develops, then the cursor, pushed by a greater pressure difference, assumes a position close to the second position while coinciding with it, leaving clear a largepassage cross-section, thus not causing a pressure drop that would appreciably reduce the volume of water drawn, whereas, on the other hand, under these conditions, the thermostatic mixing device does not tend to display any unstable performance. The valve thus automaticallyxe2x80x94and independently of the kind of thermostatic mixing device involvedxe2x80x94brings about the same effect that can be achieved by an appropriate maneuver employed by the user according to the teaching in Italian Patent Application TO 99 A 000 455.
An automatic valve, according to the invention, can be inserted in only one water supply pipeline or in both, but preferably it is inserted only in the cold water supply pipeline.
The second object of the invention is achieved when the cursor in said first position occludes the seat totally. In this case, as a matter of fact, when no water is drawn or if the flow tends to assume a direction opposite to the normal direction, the cursor, shifting into said first position, completely occludes said seat so that the valve works like a nonreturn valve.
The second object of the invention can also be achievedxe2x80x94even if the cursor in said first position does not totally occlude said seatxe2x80x94by inserting in the valve an element, for example, a flexible and elastic membrane arranged so as to occlude at least one passage opening, while the flow tends to assume a direction opposite to the normal direction.
The structure of the valve, according to the invention, can assume various configurations that are specifically indicated in the following description and in the subclaims. These and other features, objects and advantages of the object of this invention will appear more clearly in the following description of some embodiments, constituting nonrestrictive examples, with reference to the attached drawings.